The present disclosure relates, in various embodiments, to a novel protective barrier layer composition for the protection of organic electronic devices from adverse environmental effects such as exposure to light, oxygen, or moisture, or a combination of these factors
Thin film transistors (“TFT”s) are fundamental building blocks of electronic circuits. Structurally, TFT comprises a supporting substrate, three electrically conductive electrodes (gate, source and drain electrodes), a semiconductor layer, and a dielectric layer. For operational stability and extended life, it is often necessary to protect the TFTs from adverse environmental effects with a protective barrier layer. Various TFT configurations are possible to enable proper functioning of TFTs in various electronic applications. Exemplary configurations are depicted in FIGS. 1 through 4. The semiconductor is electrically insulating when the transistor is in its switched-off state, when no bias voltage is applied to the gate electrode. When a bias voltage is applied to the gate electrode, the transistor is switched on, an electric current flows between the source and the drain electrodes through the semiconductor layer. At a given source-drain electric field, the current flowing between the source-drain electrodes can be modulated by the bias voltage applied to the gate electrode
Exposure to various environmental conditions can adversely affect the performance of an electronic device such as organic TFT (OTFT). For example, the organic semiconductor layer can be damaged by light, oxygen and moisture, etc. degrading its electrical properties. Consequently, TFTs need to be protected from these environmental conditions with a protective barrier or encapsulation layer. For inorganic material-based TFTs such as amorphous silicon TFTs, this is traditionally done by passivation with a vacuum deposited inorganic oxide layer (e.g., silicon nitrides). For low-cost OTFTs, a liquid-processable barrier layer would be preferable to lower manufacturing cost.
Prior-art OTFT barrier or encapsulation layers consist of polymers like polyvinylphenol, polymethylmethacrylate (PMMA), polyethylene, polyethyleneterephthalate, and mixtures of these polymers. However, these polymers have high oxygen and water permeability and cannot function as satisfactory barrier layers for OTFTs. Other prior-art barrier approaches include multilayer encapsulations containing dessicants or oxygen scavengers and an in-situ polymerized polymer layer. However, these approaches are also not very effective in protecting OTFTs against environmental conditions. For example, dessicants have a finite capacity to absorb moisture and will cease to function once they are saturated with moisture. Multilayer barrier layers are more costly to apply to OTFTs than a single barrier layer and are therefore less preferred.